In recent years, high integration and high density in semiconductor device demands smaller and smaller wiring patterns or interconnections and also more and more interconnection layers. Multilayer interconnections in smaller circuits result in greater steps which reflect surface irregularities on lower interconnection layers. An increase in the number of interconnection layers makes film coating performance (step coverage) poor over stepped configurations of thin films. Therefore, better multilayer interconnections need to have the improved step coverage and proper surface planarization. Further, since the depth of focus of a photolithographic optical system is smaller with miniaturization of a photolithographic process, a surface of the semiconductor device needs to be planarized such that irregular steps on the surface of the semiconductor device will fall within the depth of focus.
Thus, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. One of the most important planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing, while a polishing liquid containing abrasive particles such as silica (SiO2) or ceria (CeO2) therein is supplied onto a polishing surface of a polishing pad, a wafer is brought into sliding contact with the polishing pad, so that the wafer is polished.
A polishing apparatus for performing CMP has a polishing table that supports a polishing pad thereon, and a top ring for holding a wafer. In the case where the wafer is polished using such polishing apparatus, the top ring holds the wafer and presses the wafer against the polishing pad at a predetermined pressure. At this time, the polishing table and the top ring are moved relative to each other to bring the wafer into sliding contact with the polishing pad to thereby polish a surface of the wafer.
In the above-described polishing apparatus, because a frictional force is generated between the wafer and the polishing pad during polishing, this frictional force is received by the retaining ring to prevent the wafer from being slipped out of the lower part of the top ring. Further, the retaining ring presses the polishing pad to deform the polishing pad, so that a polishing pressure applied to an edge portion (peripheral portion) of the wafer is adjusted and thus the polishing amount of the edge portion (peripheral portion) of the wafer is controlled by the deformation of the polishing pad.
In the polishing apparatus described above, the wafer is brought into contact with an inner wall surface of the retaining ring at the time of top ring stabilizing, and chipping may occur. Here, “top ring stabilizing” refers to an operation to stabilize a pressure of an air bag (pressure chamber) of the top ring by adding a polishing process before starting actual process polishing. Since the retaining ring is made of a resin such as PEEK or PPS, when chipping of the wafer occurs, a fragment of the wafer cuts into (bites into) the inner wall of the retaining ring. As the number of polished wafers increases, the fragment of the wafer which has cut into the inner wall surface of the retaining ring falls onto the polishing pad, thus causing a scratch of the wafer surface.